1. Field of the Invention
The invention relates to capacitive couplers for non-contacting or contactless signal and data transmission, in particular to capacitive rotating transmission devices like rotary joints. Such transmission devices may be used in computer tomography scanners, also called CT scanners.
2. Description of Relevant Art
Capacitive rotating couplers, also called capacitive rotary joints are used to couple signals and data between parts rotating against each other. For example, in CT scanners, a rotating x-ray tube and an x-ray detector generate high-speed imaging data. The data may be transmitted from the rotating part to the stationary part. Furthermore, control signals for controlling the device and specifically the power supply of the x-ray tube may be transmitted from the stationary to the rotating part and vice versa. Many further applications exist where there is the need to transmit control signals or data between a rotor and a stator like in windmills, revolving transfer machines, bottling plants, packaging machines or placement heads of insertion machines.
A capacitive rotary joint for CT scanners is disclosed in U.S. Pat. No. 5,600,697. A large diameter rotating ring carries a differentially driven strip line guiding a signal along this circumference of the ring. At the stationary side, there is a capacitive coupler picking up the signal from the near field of the strip line. The receiving coupler comprises two lines held orthogonally to the transmission line. To obtain a sufficient coupling efficiency and therefore a sufficient signal level at the receiver, the coupler must be mounted in close proximity to the strip line.
A bidirectional capacitive coupler is disclosed in US 2013/0214614. Here, the channels for the communication from the rotating to the stationary side and vice versa are interleaved.
A noise immune capacitive coupler is disclosed in U.S. Pat. No. 6,956,450 B1. Here, the transmission line is not a strip line, but it is a low pass filter structure, having a pair of transmission line conductors, suitable to suppress high frequency noise. It is terminated at its ends with the characteristic impedance of the line. Due to the pattern, the structure is wider than a strip line with a comparable characteristic impedance. This results in a larger coupling capacitance with a similar coupler layout compared to a strip line.